1. Field of the Invention
The invention relates to a wheel hub for vehicles having a built-in brake assembly for stopping and parking the vehicle. For this, the wheel hub comprises a hollow axle casing fixed to a vehicle frame, a hollow axle housing rotatably mounted on the axle casing and carrying a vehicle wheel rim, a planetary gearing and a multi-plate friction type wet brake both being coupled to a drive shaft driven by a wheel hub of the vehicle, wherein the multi-plate friction type wet brake having inner brake plates, outer brake plates and a brake piston displaceable in axial direction is arranged in its entirety within a ring gear support member splined on the periphery of said axle casing without rotation, and the brake for parking the vehicle has a piston and a spring assembly.
2. Description of the Related Art
U.S. Pat. No. 5,088,967 describes a driven axle assembly of heavy duty vehicles such as muckshifters, mining machines, agricultural power machines and vehicles for handling and transporting materials, which has a planetary gearing and a multi-plate friction type wet brake. This solution is able to cope with the high loads and stresses applied on driven axle assemblies of vehicles as mentioned above, but it is lacking of a parking brake serving to leave the wheels of the vehicle in braked position when it is out of operation as well as to provide safety brake action when the normal operational brake has malfunction.
It is not unusual to provide an auxiliary parking brake assembly for wheel hubs of the driven axle assemblies of this type, i.e. wherein a multi-plate friction type wet brake is arranged for the purpose of the operational braking system of the vehicle. French Patent Application No. 2 519 091 has a parking brake with a piston and a spring assembly, wherein the springs are formed as cup springs arranged longitudinally in xe2x80x9cseriesxe2x80x9d with the operational brake. Therefore, the wheel hub has enlarged constructional length. Further, the brake plates of the wet operational brake are connected without any gearing directly onto the wheel hub, thus, the braking force in relation to the force applied onto the brake piston is extremely low. As a result, enlarged number of brake plates and brake piston pressure are necessary and the reaction forces within the hub result in enlarged loads on the gears and bearings.
The arrangement of operational brake and parking brake is quite similar in German Patent Specification No. DE 32 43 117, however, the two brakes are at the two extremities of the wheel hub. Therefore, complicated mechanism is necessary to lead the braking action from the parking brake to the brake plates of the multi-plate friction type wet brake. Quite unusually, both the outer brake plates and the inner brake plates are revolving and the braking action is resulting from the difference between the two rotational speeds. Therefore, the braking efficiency of this solution is quite low.
In the solution as shown in U.S. Pat. No. 4,576,256, the outer diameter of the whole wheel hub is considerably enlarged to be able to arrange the cup spring bundle and the hydraulic piston of the parking brake within the axle casing. Since the axle housing is rotatable against the axle casing, the bearing between them must have unusually large diameters. To reduce the length of the hub, the bearings are in near vicinity to each other, all these reducing the stability and the stiffness of the assembly. The constructional parts to lead the braking force of the parking brake from within the axle casing to the brake plates are quite complicated and ineffective because of the diametrical differences between the two brake assemblies.
Further to these disadvantages, it is characteristic for all known solutions that they are not equipped with means for manually de-activating the parking brake if the vehicle is out of function because of any reason. If the engine or the hydraulic system of the vehicle are brought to standstill or have any malfunction, the vehicle cannot be moved on its wheels since the braking action of the parking brake cannot be eliminated from outside the hub. Since the wheel hubs with driving gearing, multi-plate friction type wet brake and parking brake in the inside are most commonly used with heavy duty vehicles, the need to overcome this disadvantage is quite urgent.
The main objective of the present invention is to provide a wheel hub for the driven axle of vehicles wherein the advantages of the well proved axle assemblies with driving gearing and multi-plate friction type wet brake in the inside can be preserved when combined with a parking brake in the wheel hub without increase of complexity, production and operation costs and decrease of duration, load bearing capacity and reliability. At the same time, the wheel hub shall be suited for de-activating the parking brake when the vehicle is out of operation.
The basic idea of this invention is to integrate the parking brake into the operational brake of the wheel hub and to provide access to the activating unit of the parking brake from the outside of the wheel hub.
Hence, according to the invention, a wheel hub for vehicles having a built-in brake assembly for stopping and parking the vehicle comprises a hollow axle casing fixed to a vehicle frame, a hollow axle housing rotatably mounted on the axle casing and carrying a vehicle wheel rim, a planetary gearing and a multi-plate friction type wet brake both being coupled to a drive shaft driven by a driving unit of the vehicle, wherein the multi-plate friction type wet brake having inner brake plates, outer brake plates and a brake piston displaceable in axial direction is arranged in its entirety within a ring gear support member splined on the periphery of said axle casing without rotation, and the brake for parking the vehicle has a piston and a spring assembly.
The improvement is in that the piston and the spring assembly of the brake for parking the vehicle are arranged within the ring gear support member, they impact on the brake piston of the multi-plate friction type wet brake, on one hand, and on the ring gear support member, on the other, and the brake for parking the vehicle has means for manually de-activating said parking brake from outside the hub.
Various optional or preferred features are set out in the detailed description forming part of this specification.
Thus, in one exemplified embodiment of this invention, the piston of the parking brake is formed as an annular piston moveably arranged on the outer periphery of a disk holding the ring gear support member against the axle casing and fixed to the axle casing. Therein, it may be preferred, that a pressure chamber is formed between the piston and the disk, and the piston has a radially inwardly extending flange sealed against the disk and the disk has a radially outwardly extending flange sealed against the piston.
It is also preferred, according to the invention, that the spring assembly of the parking brake has a series of helical springs arranged parallelly to each other and the driving shaft on a diameter exceeding the inner diameter of the piston of the parking brake. In this case, the piston may have an annular groove serving as spring cup receiving the springs of the spring assembly of the parking brake and lying with its outer surface against the brake piston.
A further preferred embodiment is wherein the spring assembly of the parking brake has at least one annular cup spring lying against the brake piston and/or said piston of said parking brake, on one hand, and the support member, on the other.
It is still another preferred embodiment, wherein the means for manually de-activating said parking brake has means to urge the piston of the parking brake against the ring gear support member.
Most preferably, at least one through-bore passing through an outer cover of the hub, a planetary carrier of the planetary gearing, the inner brake plates and the piston as well as at least one screw in threaded connection with the support member coaxially with the through-bore are provided, and a head of each screw lies against a flange of the piston to move the piston towards the support member when the screw is screwed into the support member, and each through-bore is blanked by a screw in the outer cover, respectively.